1. Field of the Invention
The present invention relates to an information recording/reproduction apparatus for recording/reproducing information using an optical recording medium such as an optical card and, more particularly, to an information recording/reproduction apparatus having a device for detecting recording power of a laser beam when information is recorded and controlling a power of the laser beam.
2. Description of the Related Art
In a conventional information recording/reproduction apparatus for recording/reproducing information using an optical recording medium such as an optical card, a laser beam is emitted from a semiconductor laser is concentrated by a condenser to form an optical spot. The optical spot traces a number of information tracks arranged in parallel to one another in a predetermined region on the surface of the optical card, whereby recording/reproducing of information is performed.
It is known that the ratio of output power to drive current in the semiconductor laser varies with its surrounding temperature, secular changes or the like. In the conventional information recording/reproduction apparatus, therefore, output power of a laser beam is detected and compared with predetermined target power, and a difference between them is fed back to a drive circuit for driving the semiconductor laser to stably output a laser beam having power approximate to the target power.
Published Unexamined Japanese Patent Application No. 58-40878 discloses a method of detecting a change in characteristics of a semiconductor laser and controlling output power of the semiconductor laser. This method considerably facilitates the control of the output power of the semiconductor laser since the output power is usually set to a fixed value when data is read in. However, when data is written in (recorded), an output of the semiconductor laser is usually modulated. For this reason, there occurs a drawback in which the output of the semiconductor laser cannot be controlled unless a circuit for detecting recording power is large in size in order to detect the recording power during the recording of data. Further, there occurs another drawback in which, if the output power of an optical head is changed to recording power in a direct-current manner when an optical card is set, the optical card will be damaged.
To eliminate the above drawbacks, Published Unexamined Japanese Patent Application No. 61-253651 discloses a technique of moving an optical head outside a recording region of an optical recording medium, emitting a laser beam under recording power in a direct-current manner, and detecting the recording power. Since, however, the optical head has to move outside the recording region, it takes more time to control the recording power.
Applicant proposes in Published Unexamined Japanese Patent Application No. 3-122835 discloses a method of making an amount of radiation per unit of area on a recording medium smaller than that in recording of data so that recording power can be generated without moving an optical head outside a recording region, thereby to prevent the recording medium from being damaged. It is however necessary to reset tracking or focusing after the recording power is detected, and additional time therefor is required.